Diabetic kidney disease (DKD) occurs in 30-40% of people with type 2 diabetes. People with diabetes and reduced estimated glomerular filtration rate (eGFR <60 ml/min/1.73m2) are at particularly high risk of end-stage renal disease (ESRD) as well as cardiovascular disease and death. Despite intensive glycemic control and renin angiotensin system (RAS) inhibition, the rates of progression to ESRD and death remain high. Development of new therapies targeting this DKD stage requires greater understanding of the mechanisms causing DKD progression, particularly at this stage of disease. The overall goal of this proposal is to identify the biologic pathways that are associated with progression from reduced eGFR to ESRD in type 2 diabetes. We propose to utilize a state-of-the-art, targeted, quantitative proteomics platform to quantify expression of 179 proteins from 12 biologically promising candidate pathways prior to progression from reduced eGFR to incident ESRD or 50% drop in eGFR. These pathways are selected because they have extensive support from DKD animal models as well as evidence of involvement in advanced human DKD, but have not been previously evaluated at this stage of human DKD. Using immunoassays and quantitative targeted assays from our recently completed Human Selected Reaction Monitoring Atlas (a library of peptides enabling quantitative proteomics for 20,300 human proteins), we examined urine concentration of 28 proteins from four of the above 12 candidate pathways. Our preliminary data suggests that the concentrations of 25 of these proteins are markedly abnormal, consistent with expected dysregulation of their corresponding pathways at the time of overt DKD. We hypothesize that a subset of the 12 targeted pathways are dysregulated at the time of reduced eGFR and are associated with progression to ESRD. To test this hypothesis, we propose a case-control study nested within a type 2 diabetes sub cohort of the Chronic Renal Insufficiency Cohort (CRIC) Study, with subsequent validation in the Seattle Kidney Study (SKS). We will compare urine concentration of 179 proteins from 12 key DKD pathways in CRIC participants with diabetes and reduced eGFR who do or do not progress to incident ESRD or 50% loss of eGFR during follow-up. We will use these novel measurements and the corresponding clinical data to test the following hypotheses: Aim 1. To identify the proteins and corresponding pathways which are altered in people with diabetes and reduced eGFR and are associated with DKD progression. Aim 2. To validate the proteins and pathways associated with DKD progression in the CRIC study (Aim 1) in a second cohort, the Seattle Kidney Study (SKS).